Oklahoma Electrical Practice Exam

What is the approximate voltage drop of a 540 foot run if coated 4/0 copper at 480v single phase with a load of 200a?

1. 10.5 volts

2. 11.5 volts

3. 12.5 volts

4. 13.5 volts

The correct answer is: 13.5 volts

To determine the voltage drop in a given electrical system, you can use the formula: \[ \text{Voltage Drop (V)} = \frac{2 \times L \times I \times R}{1000} \] where: - \( L \) is the one-way length of the conductor in feet, - \( I \) is the load current in amperes, - \( R \) is the resistance of the conductor in ohms per thousand feet. For a 4/0 copper conductor, the resistance is approximately 0.00025 ohms per foot. Therefore, when considering the length of 540 feet: 1. Calculate total length for the round trip: \( 2 \times 540 \) to account for both the outgoing and returning paths. 2. The load is 200 A, and using the resistance figure, we multiply the total run length by the resistance per foot and then by the load current. Plugging in the values: 1. \( R \) for coated 4/0 copper is approximately 0.1 ohms per 1000 feet. 2. Thus, \( L = 540 \text{ feet} \), and resistive drop becomes: \[ \text